The present invention relates to a flowmeter for measuring the flow rate of liquid or air. The present invention relates to means for measuring a flow rate value in an accurate manner even when there is a variation in pressure or temperature.
Conventionally, such a type of flowmeter is known, for example, in Japanese Laid-Open Publication No. 9-15006. As shown in FIG. 64, the flowmeter includes: a sampling program 2 for reading a measurement value, at an interval having a predetermined first sampling time, from an analog flow sensor 1 that measures the flow rate of gas; a consumed gas amount calculation program 3 for calculating the flow rate of consumed gas at a predetermined time; a mean value calculation program 4 for calculating the mean value of measurement values, which are read from the analog flow sensor at the first sampling time, at an interval of a second sampling time within a predetermined time period; a pressure variation frequency estimation program 5 for estimating the frequency of a pressure variation based on an output of the flow sensor; and a RAM 6 which functions as a memory. Herein, reference numeral 7a denotes a CPU for executing the programs, and reference numeral 7b denotes a ROM for storing the programs. In such a structure, a measurement process is performed such that the predetermined measurement time is equal to or longer than a single cycle of the vibration frequency of a pump or is a multiple of the cycle. Averaging is performed to suppress variation in the flow rate.
As another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 10-197303 is known. As shown in FIG. 65, the flowmeter includes: flow rate detection means 8 for detecting the flow rate; frequency detection means 9 for detecting the frequency of a variation of a flow; and measurement time set means 10 for setting the measurement time for flow rate detection to about a multiple of one cycle of the variation frequency. Herein, reference numeral 11 denotes flow rate calculation means; 12 denotes measurement start means; 13 denotes signal processing means; and 14 denotes a flow rate. With this structure, the flow rate is measured in accordance with the frequency of a variation waveform, whereby a correct flow rate measurement is achieved within a short time period.
As still another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 11-44563 is known. As shown in FIG. 66, the flowmeter includes: flow rate detection means 15 for detecting the flow rate; variation detection means 16 for detecting a variation waveform of the flow rate of fluid; pulse measurement means 17 for starting the measurement of the flow rate detection means when an alternating component of the variation waveform is in the vicinity of zero; and flow rate calculation means 18 for processing a signal from the flow rate detection means. Herein, reference numeral 19 denotes a signal processing circuit; 20 denotes a time measurement circuit; 21 denotes a trigger circuit; 22 denotes a transmission circuit; 23 denotes a comparison circuit; 24 denotes an amplification circuit; 25 denotes a switch; 26 denotes a measurement start signal circuit; and 27 denotes start-up means; 28 denotes a flow path. In this structure, the flow rate near the average of the variation waveforms is measured, whereby a correct flow rate measurement is achieved within a short time period.
As yet another conventional example, the invention disclosed in Japanese Laid-Open Publication No. 8-271313 is known. As shown in FIG. 67, whether or not a flow rate value has been detected in flow sensor measurement (29) is confirmed (30). Until a flow rate is confirmed to have been detected, the process does not proceed, and the measurement with the flow sensor is continued. Once a flow rate is found, it is determined whether or not the flow rate Q is equal to or higher than a predetermined value (31). When the flow rate Q is equal to or higher than the predetermined value, it is further determined whether or not the pressure variation surpasses a predetermined value Cf (32). When the pressure variation does not surpass a predetermined value Cf, measurement 34 is performed with a piezoelectric film sensor of a fluidic flowmeter. When the pressure variation surpasses a predetermined value Cf, it is confirmed if the pressure variation surpasses a second predetermined value (33). When the pressure variation surpasses the second predetermined value, the measurement (34) is performed with the piezoelectric film sensor of the fluidic flowmeter. When the pressure variation does not surpass the second predetermined value, the measurement (29) is performed with the flow sensor.
As shown in FIG. 68, ultrasonic wave transducers 51 and 52 are provided in a flow rate measurement section 50 so as to oppose the direction of a flow. A control section 53 starts a timer 54, and simultaneously, outputs a transmission signal to a driver circuit 55. An ultrasonic wave is transmitted from the ultrasonic wave transducer 51 which received an output of the driver circuit 55. The ultrasonic wave is received by the ultrasonic wave transducer 52. A reception detection circuit 56 which received an output of the ultrasonic wave transducer 52 detects the ultrasonic wave and stops the timer 54. By such an operation, a time (t1) spent from a time when an ultrasonic wave is transmitted from the ultrasonic wave transducer 51 to a time when the wave is detected by the ultrasonic wave transducer 52 is measured. Next, a switching circuit 58 is operated based on a signal from the control section 53, such that the driver circuit 55 and the ultrasonic wave transducer 52 are connected, and the reception detection circuit 56 and the ultrasonic wave transducer 51 are connected. Under this state, transmission and reception of an ultrasonic wave is performed again to measure a time (t2) spent from a time when an ultrasonic wave is transmitted from the ultrasonic wave transducer 52 to a time when the wave is detected by the ultrasonic wave transducer 51. Based on the two propagation times (t1) and (t2), a calculation section 57 calculates the flow rate from a difference between inverse numbers of the propagation times.
As a conventional example of this type of flowmeter, the invention disclosed in Japanese Laid-Open Publication No. 6-269528 is known.
However, in the first of the above conventional inventions, the gas flow rate is measured by using a mean value. Therefore, measurement over a long time period is necessary in order to obtain a reliable mean value, and hence such flow rate measurement cannot be performed within a very short space of time. In the second of the above conventional inventions, measurement cannot deal with a variation in frequency. In the third and fourth conventional inventions, the method for measuring the flow rate must be changed according to the presence/absence of a pressure variation, and it is necessary to provide two means, pressure measurement means and flow rate measurement means. In the first to forth inventions, when any abnormality occurs, measurement either cannot be performed, or can be performed but with decreased accuracy.
Still further, in the above conventional structures, when receiving a signal, if noise which is in synchronization with the measurement frequency or transmission frequency of an ultrasonic wave is present, the noise is superposed on the signal always at the same phase when the propagation time is the same. The noise is counted as a measurement error, and accordingly, correct measurement cannot be performed. Moreover, when the propagation time is varied due to a variation in temperature or the like, the phase at which noise is superposed is varied, and accordingly, a measurement error is varied. As a result, a correction value cannot be stabilized. Furthermore, since the measurement resolution is determined based on the resolution of the timer 54, simply averaging the measurement values cannot increase the accuracy of measurement. Thus, it is necessary to increase the resolution of the timer 54 in order to perform measurement which requires the resolution. When the operation clock of the timer 54 is increased so as to have a high frequency, various problems occur, i.e., an increase in current consumption, an increase in high-frequency noise, and an increase in size of circuitry. Thus, there exists an objective to increase the resolution of measurement with a timer which operates at a low frequency in order to increase the measurement accuracy.
In the fifth conventional invention, a delay means is inserted between a control section and a drive circuit, and the amount of delay is changed such that a reflected wave is avoided. In this way, an effect by the reflected wave is reduced. For example, the ultrasonic wave transducer at a receiving side is vibrated due to noise generated when the ultrasonic wave is transmitted. Thus, to a variation in the signal-reception detecting time, which is caused by superposition of reverberation of this vibration on the ultrasonic wave signal, cannot be decreased.
The present invention seeks to solve the above problems. A first objective of the present invention is to set an optimum number of times that the measurement is repeated according to a variation of a flow by detecting a variation frequency using software but without using additional variation detecting device, and successively changing the number of repetition times. Further, it is sought to achieve a measurement flow rate in a reliable and accurate manner within a very short space of time even when there is a change in pressure variation and variation frequency. A second objective of the present invention is to instantaneously perform highly accurate flow-rate measurements by switching so as to detect a variation with transmission/reception means without using an additional variation detecting device and performing measurement processing in synchronization with a variation. A third objective of the present invention is to perform highly accurate flow-rate measurement, even when any abnormality occurs in the measurement process, by quickly detecting the abnormality with measurement monitoring means and appropriately processing the measurement. A fourth objective of the present invention is to perform flow-rate measurement in a reliable and accurate manner within a very short space of time by using instantaneous flow rate measurement means and digital filter means. A fifth objective of the present invention is to measure a flow rate value with a high accuracy even when there is a variation in temperature.
In order to solve the above problems, a flowmeter of the present invention includes: transmission/reception means provided in a flow path for performing transmission/reception using a state change of fluid; repetition means for repeating the transmission/reception; time measurement means for measuring a time or propagation repeated by the repetition means; flow rate detection means for detecting a flow rate based on a value of the time measurement means; and number-of-times change means for changing to a predetermined number of repetition times. The number of repetition times is changed to a number suitable for a variation such that an influence of a variation of a flow can be suppressed. As a result, reliable flow rate measurement with a high accuracy can be achieved.
The flowmeter includes a pair of transmission/reception means which utilize propagation of an ultrasonic wave as the state change of fluid. Thus, by using the sonic wave transmission/reception means, propagation of a sonic wave can be performed even when a state change occurs in the fluid. Moreover, by changing the number of repetition times to a number suitable for the variation, reliable flow rate measurement with a high accuracy can be achieved.
The flowmeter includes transmission/reception means which utilizes propagation of heat as the state change of fluid. Thus, by using the heat transmission/reception means, propagation of heat can be performed even when a state change occurs in the fluid. Moreover, by changing the number of repetition times to a number suitable for the variation, reliable flow rate measurement with a high accuracy can be achieved.
The flowmeter includes: elapsed time detection means for detecting halfway information for a propagation time which is repeatedly measured by the repetition means; frequency detection means for detecting a frequency of a flow rate variation from information of the elapsed time detection means; and number-of-times change means for setting a measurement time so as to be substantially a multiple of the frequency detected by the frequency detection means. Thus, it is not necessary to provide specific detection means. Before flow rate detection is performed, the frequency of a variation is detected from halfway information of the time measurement means, and the measurement time can be set so as to be a multiple of a cycle of the frequency. As a result, reliable flow rate measurement with a high accuracy can be achieved.
The flowmeter includes: data holding means for holding at least one or more propagation time of repeatedly-performed transmission/reception which is obtained by the elapsed time detection means; and frequency detection means for detecting a frequency by comparing the data held by the data holding means and measured propagation time data. Time measurement information at each moment is held and compared by the data holding means, whereby the frequency can be detected.
The number-of-times change means is operated in predetermined processing. Since the number-of-times change means is operated only when predetermined processing is performed, the processing in the number-of-times change means can be limited to the required minimum. Thus, the amount of consumed power can be considerably reduced.
The number-of-times change means is operated at each predetermined flow rate measurement. Thus, the number of repetition times is changed at every predetermined flow rate measurement, whereby the flow rate can be measured with a high accuracy in a stable manner even in a flow that varies greatly.
The number-of-times change means is performed before flow rate measurement processing. Since the number of repetition times is set to a predetermined number of times before flow rate measurement is performed, the flow rate measurement can be performed with a high accuracy in a reliable manner.
Predetermined processing includes operations of abnormality determination means for determining abnormality in flow rate from the measured flow rate; and flow rate management means for managing a use state for a flow rate from a measured flow rate. Since the number of repetition times is changed only when the abnormality determination processing and the flow rate management processing are performed, the processing of changing the number of repetition times is limited to the required minimum. Thus, the amount of consumed power can be decreased.
The number of repetition times which is adjusted the frequency obtained by the frequency detection means is used in next flow rate measurement. Since the number of repetition times is used in the next measurement, it is not necessary to perform repetitious measurement for frequency detection. Thus, the amount of consumed power can be decreased.
The number-of-times change means is operated when the measured flow rate is lower than a predetermined flow rate. Since the number of repetition times is changed only when the flow rate is equal to or lower than a predetermined flow rate, but this processing is not performed when the flow rate is high, the amount of consumed power can be decreased.
A flowmeter of the present invention includes: transmission/reception means provided in a flow path for performing transmission/reception using a state change of fluid; time measurement means for measuring a propagation time transmitted/received by the transmission/reception means; flow rate detection means for detecting a flow rate based on a value of the time measurement means; variation detection means for measuring a variation in the flow path by the transmission/reception means; and measurement control means for starting measurement in synchronization with a timing of a variation of the variation detection means. Since a variation in the flow path is measured by transmission/reception means, it is not necessary to provide another sensor for detecting a variation. Thus, the size of the flowmeter can be decreased, and the structure of the flow path can be simplified. In addition, the flow rate can be measured with a high accuracy in a reliable manner within a short space of time even when a variation occurs.
The flowmeter includes a pair of transmission/reception means which utilize propagation of an ultrasonic wave as the state change of fluid. Thus, a state change of fluid can be detected by the sonic wave ok transmission/reception means. Accordingly, the measurement can be started in synchronization with a timing of variation. As a result, the flow rate can be measured with a high accuracy in a reliable manner.
The flowmeter includes transmission/reception means which utilizes propagation of heat as the state change of fluid. Thus, a state change of fluid can be detected by the heat transmission/reception means. Accordingly, the measurement can be started in synchronization with a timing of variation. As a result, the flow rate can be measured with a high accuracy in a reliable manner.
The flowmeter includes: first vibration means and second vibration means provided in a flow path for transmitting/receiving an sonic wave; switching means for switching an transmission/reception operation of the first vibration means and the second vibration means; variation detection means for detecting a pressure variation in a flow path at at least one of the first vibration means and the second vibration means; time measurement means for measuring a propagation time of a sonic wave transmitted/received by the first vibration means and the second vibration means; measurement control means for performing control where, when an output of the variation detection means shows a predetermined change, the measurement means measures a first measurement time T1 of propagation from the first vibration means at an upstream side in the flow path to the second vibration means at a downstream side in the flow path, and when the output of the variation detection means shows a change opposite to the predetermined change, the measurement means measures a second measurement time T2 of propagation from the second vibration means at a downstream side in the flow path to the first vibration means at an upstream side in the flow path; flow rate detection means for calculating a flow rate using the first measurement time T1 and the second measurement time T2. Since the measurement is performed at a time when a change in a pressure variation is inverted, the phases of the pressure variation and the timing of the measurement can be shifted. As a result, a measurement error caused by a pressure variation can be offset.
The flowmeter includes: measurement control means for performing measurement control where measurement of the first measurement time T1 is started when an output of the variation detection means shows a predetermined change and measurement of the second measurement time T2 is started when the output of the variation detection means shows a change opposite to the predetermined change, and measurement control where, in a next measurement, measurement of the first measurement time T1 is started when the output of the variation detection means shows a change opposite to the predetermined change and measurement of the second measurement time T2 is started when the output of the variation detection means shows the predetermined change; and flow rate calculation means for calculating the flow rate by successively averaging a first flow rate obtained by using the previous first measurement time T1 and previous second measurement time T2 while alternately changing start of measurement and a second flow rate obtained by using next first measurement time T1 and next second measurement time T2. Thus, the timing for measurement is changed as described above in order to perform measurement for the first measurement time T1 and the second measurement time T2. As a result, even when a pressure variation is asymmetrical between a high pressure side and a low pressure side, an influence of such a pressure variation can be offset.
The flowmeter includes repetition means for performing transmission/reception a plurality of times. Thus, averaging can be performed by increasing the number of times of measurement, and as a result, reliable flow rate measurement can be performed.
The flowmeter includes repetition means for performing transmission/reception a plurality of times over a time period which is a multiple of a variation cycle. Thus, a pressure variation can be averaged by measuring according to the variation frequency. As a result, a stable flow rate can be measured.
The flowmeter includes repetition means for starting transmission/reception measurement when an output of the variation detection means shows a predetermined change and repeating the transmission/reception measurement with a sonic wave until the output of the variation detection means shows the same change as the predetermined change. Thus, the start and stop of the measurement can be made conformable to the frequency of a pressure variation. Therefore, a variation frequency can be measured, and a pressure variation is averaged. As a result, a stable flow rate can be measured.
The flowmeter includes selection means for switching a case where the first vibration means and second vibration means are used for transmission/reception of a sonic wave and a case where the first vibration means and second vibration means are used for detection of a pressure variation. Thus, at least one of the first vibration means and the second vibration means is used for pressure detection. As a result, both the flow rate measurement and the pressure measurement can be simultaneously achieved.
The flowmeter includes variation detection means for detecting a component of an alternating component of a variation waveform which is in the vicinity of zero. Thus, a variation is detected in the vicinity of a zero component of the variation, and hence the measurement can be started in the vicinity of zero variation within a time to perform flow rate measurement. Therefore, by performing the flow rate measurement within a time when a variation is small, the measurement can be stabilized even when a variation occurs in a fluid.
The flowmeter includes: frequency detection means for detecting the frequency of a signal of the variation detection means; and measurement control means for starting measurement only when the frequency detected by the frequency detection means is a predetermined frequency. Thus, by starting the measurement only when the frequency is a predetermined frequency, measurement can be performed when a predetermined variation occurs. As a result, a stable flow rate can be measured.
The flowmeter includes detection cancellation means for automatically starting measurement after a predetermined time period when a signal of the variation detection means is not detected. Thus, even after a variation disappears, the flow rate can be automatically measured when a predetermined time arrives.
The transmission/reception means and the first and second vibration means include piezoelectric transducers. Thus, when the piezoelectric transducer is used, an ultrasonic wave is used for transmission/reception while a pressure variation can be detected.
A flowmeter of the present invention includes: transmission/reception means provided in a flow path for performing transmission/reception using a state change of fluid; repetition means for repeating signal propagation by the transmission/reception means; time measurement means for measuring a propagation time during repetition by the repetition means; flow rate detection means for detecting a flow rate based on a value of the time measurement means; variation detection means for detecting a fluid variation in a flow path; measurement control means for controlling each of the above means; and measurement monitoring means for monitoring abnormality in each of the above means. Thus, when there is a variation in a flow in the flow path, the flow rate is measured according to the variation, while abnormality can be quickly detected by the measurement monitoring means. Accordingly, handling of abnormality can be correctly performed, and a measured value becomes stable. As a result, the flow rate can be measured with a high accuracy, and the reliability of the measurement can be improved.
The flowmeter includes: a pair of transmission/reception means which utilize propagation of an ultrasonic wave as the state change of fluid. Since a sonic wave is used, the flow rate measurement can be performed even when there is a variation in fluid. Further, handling of abnormality can be correctly performed by the measurement monitoring means. As a result, the reliability of the measurement can be improved.
The flowmeter includes transmission/reception means which utilizes propagation of heat as the state change of fluid. Since heat propagation is used, the flow rate measurement can be performed even when there is a variation in fluid. Further, handling of abnormality can be correctly performed by the measurement monitoring means. As a result, the reliability of the measurement can be improved.
The flowmeter includes: a pair of transmission/reception means provided in a flow path for transmitting/receiving a sonic wave; repetition means for repeating signal propagation of the transmission/reception means; time measurement means for measuring a propagation time of a sonic wave during the repetition by the repetition means; flow rate detection means for detecting the flow rate based on a value of the time measurement means; variation detection means for detecting a fluid variation in a flow path; measurement control means for controlling each of the above means; and measurement monitoring means for monitoring abnormality in a start signal which directs start of transmission of a sonic wave at a first output signal of the variation detection means after a direction signal of the measurement control means, and abnormality in an end signal which directs end of repetition of the transmission/reception of the sonic wave at second output signal of the variation detection means. Thus, when there is a variation in fluid in the flow path, the measurement can be performed in synchronization with the frequency of the variation, and abnormality can be detected by the measurement monitoring means. Therefore, a flow rate can be measured with a high accuracy, and a reliable measured value can be obtained. In addition, handling of abnormality can be correctly performed, and the reliability of the measured flow rate value can be improved.
The flowmeter includes measurement monitoring means for directing a start of transmission of a sonic wave after a predetermined time when a start signal is not generated within a predetermined time period after a direction of the measurement control means. Thus, even when there is no variation, and there is no start signal within a predetermined time period, the flow rate can be measured at every predetermined time, and loss of data can be prevented.
The flowmeter includes measurement monitoring means for directing start of transmission of a sonic wave after a predetermined time when a start signal is not generated within a predetermined time period after a direction of the measurement control means, and for performing measurement a predetermined number of repetition times. Thus, even when there is no variation, and there is no start signal within a predetermined time period, the flow rate can be measured for a predetermined number of repetition times at every predetermined time, and loss of data can be prevented.
The flowmeter includes measurement monitoring means which does not perform measurement until a next direction of the measurement control means when a start signal is not generated within a predetermined time period after a direction of the measurement control means. By suspending the operation until a next measurement direction, unnecessary measurement is not performed, whereby the amount of consumed power can be decreased.
The flowmeter includes measurement monitoring means which terminates reception of a sonic wave when an end signal is not generated within a predetermined time after a start signal. Since the reception of the sonic wave is forcibly terminated, the measurement is not suspended while waiting for the end signal. Thus, the measurement can proceed to a next process, and a stable measurement operation can be performed.
The flowmeter includes measurement monitoring means which terminates reception of a sonic wave and outputs a start signal again, when an end signal is not generated within a predetermined time after a start signal. Since the reception of the sonic wave is forcibly terminated, the measurement is not suspended while waiting for the end signal. Further, a start signal is output again so as to perform re-measurement. Thus, a stable measurement operation can be performed.
The flowmeter includes measurement monitoring means for stopping transmission/reception processing when abnormality occurs in the number of repetition times. Since the measurement is stopped when the number of repetition times is abnormal, only data with a high accuracy can be used to perform flow rate measurement.
The flowmeter includes measurement monitoring means which compares a first number of repetition times for measurement where a sonic wave is transmitted from a first one of the pair of transmission/reception means and received by the second transmission/reception means and a second number of repetition times for measurement where a sonic wave is transmitted from the second transmission/reception means and received by the first transmission/reception means, and again outputs a start signal when the difference between the first and second numbers of repetition times is equal to or greater than a predetermined number of times. Thus, re-measurement is performed when the number of repetition times is greatly different, whereby measurement with a high accuracy can be performed with a stable variation frequency.
The flowmeter includes repetition means for setting the number of repetition times such that a first number of repetition times for measurement where a sonic wave is transmitted from first one of the pair of transmission/reception means and received by the second transmission/reception means is equal to a second number of repetition times for measurement where a sonic wave is transmitted from the second transmission/reception means and received by the first transmission/reception means. Thus, by employing the same number of repetition times, a predetermined flow rate measurement can be performed even when a variation frequency is unstable.
The flowmeter includes measurement monitoring means for monitoring the number of times that a start signal is output again so as to be limited to a predetermined number of times or less, such that the outputting of the start signal is not permanently repeated. Thus, by limiting the number of times of re-measurement, the processing is prevented from continuing permanently. As a result, stable flow rate measurement can be performed.
The flowmeter measures a flow rate from a difference between inverse numbers of propagation times measured while repeating transmission/reception of an ultrasonic wave a plurality of number of times. Thus, when an ultrasonic wave is used, transmission/reception can be performed without being affected by a variation frequency in the flow path. Further, the flow rate is measured from the difference of inverse numbers of propagation times which are measured while repeating the transmission/reception, whereby even a variation of a long cycle can be measured by units of one cycle. In addition, the difference of the propagation times which is caused by a variation can be offset by using the difference of inverse numbers.
A flowmeter of the present invention includes: instantaneous flow rate detection means for detecting an instantaneous flow rate; fluctuation determination means for determining whether or not there is a pulse in a flow rate value; and at least one or more stable flow rate calculation means for calculating a flow rate value using different means according to a determination result of the fluctuation determination means. Thus, by determining a variation in a measured flow rate and switching the flow rate calculation means, the flow rate can be calculated by one flow rate measurement means according to the amount of the variation in a reliable manner.
A flowmeter of the present invention includes: instantaneous flow rate detection means for detecting an instantaneous flow rate; filter processing means for performing digital-filter processing of a flow rate value; and stable flow rate calculation means for calculating a flow rate value using the filter processing means. Thus, when the digital filter processing is performed, a calculation equivalent to an averaging process can be performed without using a large number of memories for storing data. Moreover, the filter characteristic can be modified by changing one variable, i.e., a filter coefficient.
The flowmeter includes stable flow rate calculation means for calculating a stable flow rate value using the digital filter processing means when the fluctuation determination means determines that there is a pulse. Thus, when a pulse occurs, a sharp filter characteristic is selected so as to render a large pulse stable, and the filter processing can be performed only when a pulse occurs.
The fluctuation determination means determines whether or not a variation amplitude of a flow rate value is equal to or greater than a predetermined value. Thus, a pulse can be determined based on the variation amplitude of the pulse, whereby the filter processing can be modified according to the variation amplitude of the pulse.
The filter processing means modifies a filter characteristic according to a variation amplitude of a flow rate value. Since the filter characteristic is changed according to the variation amplitude of a flow rate value, the filter characteristic can be quickly modified so as to be a sufficiently relaxed filter characteristic that allows a variation according to a variation in a flow rate when the variation is small, and when the variation is large, a sharp filter characteristic is selected such that a variation of the flow rate due to a pulse can be significantly suppressed.
The filter processing is performed only when a flow rate value detected by the instantaneous flow rate detection means is low. Since the filter processing is performed only when the flow rate is low, a variation of the flow rate can be quickly handled when the flow rate is high, and an influence of fluctuation which is caused when the flow rate in low can be significantly suppressed.
Filter processing means modifies a filter characteristic according to a flow rate value. Since the filter characteristic is changed according to the flow rate value, filter processing is performed only when the flow rate is low, a variation of the flow rate can be quickly handled when the flow rate is high, and an influence of fluctuation which is caused when the flow rate is low can be significantly suppressed.
Filter processing means modifies a filter characteristic according to an interval of a flow rate time of the instantaneous flow rate detection means. Thus, by changing the filter characteristic according to an interval of the flow rate detection time, the variation can be suppressed with a relaxed filter characteristic when the measurement interval is short or with a sharp filter characteristic when the measurement interval is long.
The flowmeter includes filter processing means which modifies a filter characteristic such that a cut-off frequency of the filter characteristic becomes high when the flow, rate is high, and which modifies a filter characteristic such that the filter characteristic has a low cut-off frequency when the flow rate is low. Thus, the response characteristic is increased when the flow rate is high, and the fluctuation is suppressed when the flow rate is low.
A filter characteristic is modified such that a variation amplitude of a flow rate value calculated by the stable flow rate calculation means is within a predetermined value range. Since the filter characteristic is modified such that the variation amplitude is within a predetermined value range, the flow rate variation can be suppressed so as to be always equal to or smaller than a predetermined value.
An ultrasonic wave flowmeter which detects a flow rate by using an ultrasonic wave is used as the instantaneous flow rate detection means. Thus, by using an ultrasonic wave flowmeter, an instantaneous flow rate can be measured even when a large flow rate variation occurs. Thus, from the flow rate value, a stable flow rate can be calculated.
A heat-based flowmeter is used as the instantaneous flow rate detection means. When the heat-based-flowmeter is used, an instantaneous flow rate can be measured even when a large flow rate variation occurs. Thus, a stable flow rate can be calculated from the flow rate value.
A flowmeter of the present invention includes: a flow rate measurement section through which fluid to be measured flows; a pair of ultrasonic wave transducers provided in the flow rate measurement section for transmitting/receiving an ultrasonic wave; a driver circuit for driving one of the ultrasonic wave transducers; a reception detecting circuit connected to the other ultrasonic wave transducer for detecting an ultrasonic wave signal; a timer for measuring a propagation time of the ultrasonic wave signal; a control section for controlling the driver circuit; a calculation section for calculating a flow rate from an output of the timer; and periodicity change means for sequentially changing a driving method of the driver circuit, wherein the control section controls the periodicity change means such that the frequency of flow rate measurement is sequentially changed in order to prevent the frequency of the measurement from being constant. Thus, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
A flowmeter of the present invention includes: a flow rate measurement section through which fluid to be measured flows; a pair of ultrasonic wave transducers provided in the flow rate measurement section for transmitting/receiving an ultrasonic wave; a driver circuit for driving one of the ultrasonic wave transducers; a reception detecting circuit connected to the other ultrasonic wave transducer for detecting an ultrasonic wave signal; a control section for controlling the driver circuit for a predetermined number of times so as to drive the ultrasonic wave transducers again in response to an output of the reception detecting circuit; a timer for measuring an elapsed time for the predetermined number of times; a calculation section for calculating a flow rate from an output of the timer; and periodicity change means for sequentially changing a driving method of the driver circuit, wherein, in response to receipt of an output of the reception detecting circuit, the control section changes the periodicity change means at every receipt detection of the reception detecting circuit such that the frequency is not kept constant. Thus, the periodicity change means can be operated with a plurality of settings for measurement within one flow rate measurement cycle. As a result, noise is dispersively averaged in a measurement result, and a reliable measurement result can be obtained.
The periodicity change means switchingly outputs a plurality of output signals having different frequencies; and the control section changes a frequency setting of the periodicity change means at every measurement so as to change a driving frequency of the driver circuit. Thus, by changing the driving frequency, the reception detecting timing can be changed by a time corresponding to a frequency variation of a driving signal. Thus, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The periodicity change means outputs output signals having the same frequency and a plurality of different phases; and the control section operates such that a phase setting for the output signal of the periodicity change means is changed at every measurement and a driving phase of the driver circuit is changed. Thus, by changing the driving phase, the reception detecting timing can be changed by a time corresponding to a phase variation of a driving signal. Thus, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The frequency change means outputs a synthesized signal obtained by superposing a signal of a first frequency which is an operation frequency of the ultrasonic wave transducers and a signal of a second frequency which is different from the first frequency; and the control section outputs, through the driver circuit, at every measurement, an output signal where the second frequency of the periodicity change means is changed. Thus, the periodicity of the flow rate measurement can be disturbed. As a result, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The periodicity change means switches the setting between a case where there is a second frequency and a case where there is not a second frequency. Thus, since the reception detecting timing is changed by changing the vibration of the ultrasonic wave transducer that transmits an ultrasonic wave, the periodicity of the flow rate measurement can be disturbed. As a result, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The periodicity change means changes the phase setting of the second frequency. Thus, since the reception detecting timing is changed by changing the vibration of the ultrasonic wave transducer that transmits an ultrasonic wave, the periodicity of the flow rate measurement can be disturbed. As a result, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed/averaged when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The periodicity change means changes the frequency setting of the second frequency. Thus, since the reception detecting timing is changed by changing the vibration of the ultrasonic wave transducer that transmits an ultrasonic wave, the periodicity of the flow rate measurement can be disturbed. As a result, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is never in the same phase but dispersed when the ultrasonic wave is received. Therefore, a measurement error can be decreased.
The periodicity change means includes a delay section capable of setting different delay times; and the control section changes the setting of the delay at each transmission of an ultrasonic wave or at each receipt detection of an ultrasonic wave. Thus, in one measurement operation, reverberation of an ultrasonic wave transmitted in an immediately-previous measurement and an influence of tailing of the ultrasonic wave transducers can be dispersed, whereby a measurement error can be decreased.
The cycle width changed by the periodicity change means is a multiple of a value corresponding to a variation of a propagation time which is caused by a measurement error. Thus, when the measured values for all the settings are summed up and averaged, an error can be suppressed to a minimum.
The cycle width changed by the periodicity change means is equal to a cycle of a resonance frequency of the ultrasonic wave transducers. Thus, in a value obtained by summing up and averaging the measured values for all the settings, a measurement error which may be caused by reverberation of an ultrasonic wave or tailing of the ultrasonic wave transducers is minimum. Thus, the measurement error can be decreased.
The order of patterns for changing the periodicity is the same for both measurement in a upstream direction and measurement in a downstream direction. Thus, the measurement with an ultrasonic wave transmitted toward the upstream side and the measurement with an ultrasonic wave transmitted toward the downstream side are always performed under the same conditions. Hence, even when there is a variation in the flow rate, a reliable measurement result can be obtained.
The predetermined number of times is a multiple of a change number of the periodicity change means. Thus, all the setting values of the periodicity change means are uniformly set within a single flow rate measurement operation. As a result, a reliable measurement result can be obtained.
A flowmeter of the present invention includes: a flow rate measurement section through which fluid to be measured flows; a pair of ultrasonic wave transducers provided in the flow rate measurement section for transmitting/receiving an ultrasonic wave; a driver circuit for driving one of the ultrasonic wave transducers; a reception detecting circuit connected to the other ultrasonic wave transducer for detecting an ultrasonic wave signal; a first timer for measuring a propagation time of the ultrasonic wave signal; a second timer for measuring a time period from when the reception detecting circuit detects a receipt to when a value of the first timer changes; a control section for controlling the driver circuit; and a calculation section for calculating a flow rate from outputs of the first timer and second timer, wherein the second timer is corrected by the first timer. Since the flow rate calculation is performed using a value obtained by subtracting a value of the second timer from a value of the first timer, the time measurement resolution is equal to that of the second timer. Further, since the operation time of the second timer is very short, the amount of consumed power can be decreased. Thus, a flowmeter with high resolution which consumes a small amount of power can be realized. Furthermore, a correct flow rate measurement can be achieved so long as the second timer operates in a stable manner after the correction is made until flow rate measurement is performed. Therefore, a correct measurement can be performed even when the second timer lacks long-term stability. Thus, a flowmeter with a high accuracy can be realized with ordinarily-employed parts.
The flowmeter includes a temperature sensor, wherein the second timer is corrected by the first timer when an output of the temperature sensor varies so as to be equal to or greater than a set value. Thus, even when the second timer has a characteristic which varies according to a variation in the temperature, the second timer is corrected every time a temperature variation occurs, whereby correct measurement can be performed. Furthermore, such a correction is made only when it is necessary, the amount of consumed power can be decreased.
The flowmeter includes a voltage sensor for detecting the power supply voltage of the circuit, wherein the second timer is corrected by the first timer when an output of the voltage sensor varies so as to be equal to or greater than a set value. Thus, even when the second timer has a characteristic which varies according to a variation in the power supply voltage, the second timer is corrected every time a variation occurs in the power supply voltage, whereby correct measurement can be performed. Furthermore, it is not necessary to periodically make a correction, the amount of consumed power can be decreased.
A flowmeter of the present invention includes: a flow rate measurement section through which fluid to be measured flows; a pair of ultrasonic wave transducers provided in the flow rate measurement section for transmitting/receiving an ultrasonic wave; a driver circuit for driving one of the ultrasonic wave transducers; a reception detecting circuit connected to the other ultrasonic wave transducer for detecting an ultrasonic wave signal; a control section for controlling the driver circuit for a predetermined number of times so as to drive the ultrasonic wave transducers again in response to an output of the reception detecting circuit; a timer for measuring an elapsed time for the predetermined number of times; a calculation section for calculating a flow rate from an output of the timer; and periodicity stabilizing means for sequentially changing a driving method of the driver circuit, wherein the control section controls the periodicity stabilizing means such that a measurement frequency is always maintained to be constant. With this structure, the measurement frequency is always constant even when a propagation time varies. Thus, noise which is in synchronization with a measurement frequency or a transmission frequency of an ultrasonic wave is always in the same phase when the ultrasonic wave is received regardless of a variation in the propagation time. Therefore, a measurement error can be maintained as a constant value. Accordingly, the flow rate measurement can be stabilized even when the noise has a very long periodic noise.
The control section includes periodicity stabilizing means formed by a delay section capable of setting different delay times; and the control section changes an output timing of the driver circuit by switching the delay times. Since the measurement frequency is maintained to be constant by changing the delay time, the measurement frequency can be stabilized without giving an influence to driving of the ultrasonic wave transducers.
The control section controls the driver circuit such that a measurement time is maintained to be constant-. Thus, the measurement frequency can be maintained to be constant with a simple calculation without calculating a propagation time for each ultrasonic wave transmission.